CN112752981B

CN112752981B - Method and device for carrying out a shutdown test on an inverter

Info

Publication number: CN112752981B
Application number: CN201980063348.6A
Authority: CN
Inventors: J·丹迈尔; C·卡斯伯格
Original assignee: Fronius International GmbH
Current assignee: Fronius International GmbH
Priority date: 2018-09-28
Filing date: 2019-09-24
Publication date: 2023-02-17
Anticipated expiration: 2039-09-24
Also published as: AU2019348482B2; AU2019348482A1; EP3857245A1; BR112021003804A2; EP3857245B1; US20220011365A1; CN112752981A; WO2020064740A1; EP3629041A1

Abstract

In order to be able to carry out a shutdown test on the inverter (1) with low effort, provision is made for a first point in time (t) _T ) Modulating a Trigger Signal (TS) to an alternating current (I) _AC ) Or an alternating voltage (V) _AC ) At a second point in time (t) _F ) I.e. the passage of a defined duration (t) after the start of the Trigger Signal (TS) _D ) Generating an alternating current (I) with a Fault Signal (FS) by means of an inverter (1) _AC ) Or an alternating voltage (V) _AC ) The fault signal is detected by the inverter (1) and triggers the inverter (1) to be switched off, and an alternating current (I) is determined _AC ) Or an alternating voltage (V) _AC ) Off point in time (t) _A ) Whereby, at the off-time (t) _A ) And a second point in time (t) _F ) The difference between them determines the turn-off duration (t) of the inverter (1) _Z )。

Description

Method and device for carrying out a shutdown test on an inverter

Technical Field

The invention relates to a method for carrying out a shutdown test on an inverter, which generates an alternating current and an alternating voltage at an output. The invention also relates to a device for carrying out a shutdown test on an inverter, comprising a control unit which controls the switching devices of the inverter in order to generate an alternating current and an alternating voltage at the output.

Background

The inverter is used to connect a power supply feeding the grid to the supply network. In the case of bidirectional inverters, these are also used for charging the energy store from the power supply or from the supply network. In the case of an emergency-capable inverter, the inverter can supply the stored energy to the consumer even without a supply network. The power source is, for example, a photovoltaic power generation system or one or more photovoltaic cells. But the power source may also be a wind generator, a battery or the like. Such inverters connected to the supply network are subject to strict regulations, for example by national electrical grid operators or by national legislation. In order to obtain a license for an inverter for grid operation, such an inverter must undergo different testing methods. Many of these tests are intended to ensure that the inverter must terminate the feed operation after a defined maximum time after a fault and/or must disconnect itself from the supply network. The inverter therefore already performs a monitoring function in order to detect and evaluate different fault signals and, if necessary, to disconnect the inverter from the supply network or the load. When a permissive test is to be carried out, a fault signal is connected to the output of the inverter, which can be detected by the inverter and in general the switch-off duration and a measured value can be determined, in the case of which the inverter has been disconnected from the supply network or the feed operation has been terminated. The maximum switch-off duration specified in the test standard should therefore be checked. The problem in this respect is that the point in time at which the fault signal is applied should be determined in order to be able to accurately determine the time elapsed from application to shutdown.

Up to now, a trigger signal is emitted by the inverter at the trigger output as soon as a fault signal is provided. The trigger signal can then be detected in order to detect the switch-off duration from this. The flip-flop output is however only internally accessible, since it is not needed in normal operation. Therefore, the inverter must be opened to intercept the trigger signal, which is problematic and constitutes a safety risk on the basis of the high voltage in the inverter. Since the trigger signal is time-critical, for this purpose, I/os are required which are very close to the hardware and therefore usually have a danger potential (voltage of a low protective voltage of more than 50V) or are located close to the danger potential, which is also problematic when carrying out shutdown tests, since corresponding safety precautions have to be taken. In addition, a separate trigger output must be provided for this purpose on the hardware of the inverter, which of course makes the circuit more complex and expensive.

Another known method is to use a high resolution oscilloscope to record the correlation signal. But setting the correct trigger based on measurement resolution is a considerable problem when the voltage or current changes are very small. For this reason, one must typically use very high quality oscilloscopes, which in turn makes the test more expensive.

Disclosure of Invention

The object of the present invention is therefore to provide a device and a method with which an exact triggering of the point in time of occurrence of a fault can be determined for a shutdown test on an inverter without additional hardware complexity or without additional expensive measuring equipment, in order to be able to determine the shutdown duration in a simple manner.

According to the invention, this object is achieved by the method according to the invention and the device according to the invention.

According to the method of the invention for carrying out a shutdown test on an inverter, which generates an alternating current and an alternating voltage at an output, a trigger signal is modulated onto the alternating current or onto the alternating voltage at a first point in time, wherein the starting point in time of the trigger signal is the first point in time; determining a second time point by the first time point and the defined duration; at a second point in time, i.e. after the defined time duration has elapsed after the start of the trigger signal at the first point in time, an alternating current or an alternating voltage is generated with the inverter with a fault signal which is detected by the inverter and which triggers the inverter to be switched off; and determining a switch-off time point of the alternating current or alternating voltage, whereby the switch-off duration of the inverter is determined by the difference between the switch-off time point and the second time point.

The device according to the invention for carrying out a shutdown test on an inverter has a control unit which is designed to control a switching device of the inverter for generating an alternating current and an alternating voltage at an output, and which is designed to control the switching device of the inverter at a first point in time in order to modulate a trigger signal onto the alternating current or onto the alternating voltage, wherein the starting point in time of the trigger signal is the first point in time; the control unit is designed to determine a second time point by means of the first time point and a defined time duration and to control the switching devices of the inverter at the second time point, i.e. after the trigger signal has started at the first time point for the defined time duration, in order to generate an alternating current or an alternating voltage with a fault signal; performing a safety function in the inverter, the safety function being configured for recognizing a fault signal and triggering a shutdown of the inverter; and an evaluation unit is provided, which is designed to determine a switch-off time of the alternating current or alternating voltage and to determine a switch-off duration of the inverter from a difference between the switch-off time and a second time.

Thus, after starting the shutdown test at the first point in time, a defined duration is waited for before applying the fault signal. The first point in time can be determined accurately and unambiguously by means of the trigger signal. Since the time duration is known, a second point in time at which the output of the fault signal is started can also be unambiguously determined. The switch-off time can likewise be unambiguously determined as the time at which the alternating current or the alternating voltage is zero or substantially zero. The shutdown duration, i.e., the time elapsed between the start of the fault signal and the shutdown, can thus be unambiguously and simply determined as a result of the shutdown test using this procedure. The shutdown can be carried out in any desired manner, for example by opening a disconnection point in the inverter and/or by terminating the generation of the alternating current/alternating voltage. The shutdown can also be triggered in any desired manner, for example by a control unit of the inverter.

Preferably, the alternating current generated by the inverter or the alternating voltage generated by the inverter is measured and evaluated in order to determine the first point in time and/or the switch-off point in time. This allows the shutdown test to be performed automatically, which simplifies the shutdown test.

The determination of the different points in time, in particular, is further simplified if the first point in time and/or the second point in time are synchronized to the zero crossing of the alternating current or the alternating voltage.

In a simple embodiment, the evaluation unit can be designed as an oscilloscope which records the alternating current or the alternating voltage, whereby the first time point and/or the switch-off time point can be determined.

Drawings

The invention is explained in more detail below with reference to fig. 1 to 4, which show an advantageous embodiment of the invention by way of example, schematically and without limitation. The attached drawings are as follows:

FIG. 1 illustrates one embodiment of an inverter;

fig. 2 shows a possible device for carrying out a shutdown test on an inverter; and is

Fig. 3 and 4 show possible embodiments for triggering the fault signal.

Detailed Description

Fig. 1 shows an exemplary single-phase inverter 1, which comprises a dc voltage V _DC And comprises a DC voltage side having a terminal for an AC voltage V _AC The ac voltage side of the connection terminal of (1). A DC voltage source as a power source 15, for example at least one photovoltaic module 7, is connected for a DC voltage V _DC And the inverter 1 is used for the alternating voltage V _AC Is connected to the supply network 5 or to another electrical load.

DC voltage intermediate circuit capacitor C _Z Normally associated with the DC voltage V _DC Are connected in parallel so as to make the direct voltage V _DC Smooth and stable. On the AC voltage side, can be used for AC voltage V _AC Is provided with a disconnection point 4, for example with a disconnection relay, in order to be able to disconnect the inverter 1 from the supply network 5. An output filter 3, for example, having a filter choke L and having a filter capacitance C, can be connected upstream of the disconnection point 4 in order to generate an alternating voltage V _AC And (6) smoothing. The dc voltage side may also be provided with a disconnection point. The dc voltage side of the inverter 1 is connected to the ac voltage side via a switching device 2, for example, a bridge circuit having semiconductor switches T1, T2, T3, and T4. By means of the clocked switching of the semiconductor switches T1, T2, T3, T4 of the switching device 2, an alternating voltage is generated which is desired in terms of frequency, value and phase in a known manner.The inverter 1 is usually synchronized to the grid voltage in the supply network 5.

The inverter 1 can also be designed in a multiphase manner, with a switching device 2 and, if appropriate, an output filter 3 and a disconnection point 4 being provided for each phase or with a corresponding topology of the switching device 2.

Each inverter 1 also has a control unit 10 (hardware and software) for the correct control of the semiconductor switches T1, T2, T3, T4 of the switching device 2. The control unit 6 also controls the disconnection point 4 on the direct and/or alternating voltage side in order to terminate the alternating voltage V _AC To generate or similarly terminate an alternating current I _AC Or disconnect the inverter 1 from the supply network 5. The inverter 1 also typically has an input/output interface 8, for example to receive control commands from the outside. For controlling the inverter 1, a voltage measuring unit 9 and a current measuring unit 6 are usually also provided at suitable points on the ac voltage side. The detected measured values are processed in a control unit 10 to control the inverter 1. A voltage measuring device can also be provided on the dc voltage side for measuring an intermediate circuit voltage, which can also be processed in the control unit 10.

It should be noted, however, that other topologies of the inverter 1 exist, for example, the direct voltage side and the alternating voltage side are electrically isolated by means of a transformer or by means of differently designed switching devices 2, which is not essential for the invention. The embodiment according to fig. 1 is intended merely to illustrate the invention.

As shown in fig. 2, in order to carry out a shutdown test on the inverter 1, it is usually supplied with electrical energy from a dc voltage source 11 in a laboratory environment and is connected to the supply grid 5 or to another electrical load. On the output side, the alternating current I is detected according to a measurement technique _AC Or an alternating voltage V _AC (as schematically shown by the dashed lines) and analyzed in an analysis unit 12 (hardware and/or software). The inverter 1 receives a command B for implementing a shutdown test from the test control unit 13 via the input/output interface 8. The manner in which the command B is issued depends of course on the execution of the inverter 1 and the input/output interface 8, which is however not relevant for the inventionIt is critical. For example, the input/output interface 8 may be implemented as a bus interface for a data communication bus, such as a CAN bus or an ethernet. In this case, the command B is sent to the inverter 1 as a bus message, for example. The evaluation unit 12 and the test control unit 13 can also be designed on a common piece of hardware. However, it can also be provided that the shutdown test can be selected directly on the input/output interface 8, for example on a touch screen with corresponding menu navigation, and that the command B is issued directly on the input/output interface 8, for example by the user. In this case, provision can also be made for the user to enter the menu for the test to be switched off only by entering a secret security code beforehand or by pressing a secret key combination or the like, so that this function is not accessible in normal operation.

The type of shutdown test may also be transmitted with command B. For example, a turn-off test may be performed for detecting the presence of an alternating current I _AC As the dc component of the fault signal. In this case, the command can also be used to transmit the value to be set, for example the value of the dc component, of the error signal. Other types of shutdown tests are over-voltage, over/under frequency, identified isolated grid, arcing, etc. Fault signal and alternating current I _AC By means of the switching device 2, it is produced in such a way that the switching device 2 is controlled in a suitable manner by the control unit 10. A safety function is implemented in the inverter 1, preferably in the control unit 10 or in a separate safety unit, which, for a possible fault signal, evaluates the alternating current I, for example, as a function of the voltage v measured or the current I measured in the inverter 1 _AC Or an alternating voltage V _AC . When a fault signal is detected, the inverter 1 must be automatically disconnected from the supply network 5 (for example via the disconnection point 4 or a disconnection point on the dc voltage side) or the ac voltage V must be terminated _AC AC current I _AC Is generated.

A test routine is executed in the control unit 10, for example as software on the control unit hardware, which test routine is started upon receipt of the command B. Before the generation of the fault signal, the test routine now generates a modulation to the alternating current I at a predetermined frequency and amplitude _AC Or an alternating voltage V _AC And a trigger signal TS. The frequency maximum may be onHalf the beat frequency of the device 2 is turned off (typically in the range of more than 20 kHz). The trigger signal TS should, of course, be easily and unambiguously identifiable and should influence the supply network 5 as little as possible. For example, the trigger signal TS is an ac signal having a frequency in the range of a hundred to a thousand times the grid frequency, for example, a frequency of 1kHz and an amplitude in the range of the ac current I _AC In the range of one tenth of the amplitude, e.g. 0.3A-0.5A, or at an alternating voltage V _AC In the range of one percent of the amplitude, for example 3V-10V in the case of a 230V grid voltage. Such a trigger signal can be measured and evaluated, but also simply applied to the alternating current I on a simple oscilloscope without special resolution requirements _AC Or an alternating voltage V _AC Is identified. The trigger signal TS is preferably synchronized to the alternating current I _AC AC voltage V _AC Thereby triggering a signal, e.g. at an alternating current I _AC Ac voltage V _AC Starting at the zero crossing and lasting for a certain period duration, e.g. alternating current I _AC Ac voltage V _AC X half-waves of (1), wherein x is equal to or greater than 1. The trigger signal TS does not have to be synchronized but may in principle start at any time and last for a predetermined time.

The trigger signal TS is generated by the control unit 10 by correspondingly controlling the switching device 2 and is used to indicate a subsequent fault signal FS. The time measurement until the start of the fault signal FS may be started from the start of the trigger signal TS or from the end of the trigger signal TS. If the trigger signal TS has a defined duration, the end point of the trigger signal TS is preferably used as trigger T for the fault signal FS. If, however, the trigger signal TS has no defined duration, for example if a pulse without a defined end point is applied as trigger signal TS to the alternating voltage V _AC Above, the start of the trigger signal TS is then preferably used as trigger T for the fault signal FS and the fault signal FS passes a defined time duration T after the trigger T _D And is started after being equal to or more than 0. The fault signal FS thus begins a defined time duration T after a trigger T by the trigger signal TS _D . But these two methods are of course equivalent.

This is illustrated in fig. 3 by way of example as an alternating current I _AC For the purpose of illustration (AC voltage V) _AC Of course similar). Until a point in time t _T Alternating current I generated by inverter 1 _AC Present at the output, the alternating current is fed into the supply network 5. At a first point in time t _T And at an alternating current I _AC At zero crossing, the trigger signal TS is modulated to the alternating current I _AC Here, for example, a predetermined duration t of 1kHz and 0.5A and three half-waves _D The ac signal of (1). Thus, at the time point t _T Three half-waves thereafter, i.e. at a second point in time t _F A trigger T for the fault signal FS is determined. Fault signals FS, e.g. in the presence of alternating current I _AC Or for example a frequency change, an amplitude change or a combination thereof, thus at a defined point in time t _F (t _T +t _D ) And starting.

In the embodiment according to fig. 4, at a first point in time t _T Modulating pulses to an alternating current I _AC The above. Until a point in time t _T Alternating current I generated by inverter 1 _AC Thus, at the output, the alternating current is fed into the supply network 5. At the point of time t of the pulse _T The detectable start serves as a trigger T, wherein in this example the point in time T _T Out of synchronism to alternating current I _AC Upper, but at any point in time. At a defined duration t _D After that, a fault signal FS, e.g. an alternating current I _AC At a defined second point in time t _F (t _T +t _D ) And starting.

Now, the time point t will be described in detail with reference to fig. 3 and 4 _F Time from measurement.

Accordingly, the time measurement is at the time point t _F With the start of the fault signal FS and at the time t _A At the point in time at which the inverter 1 is disconnected from the supply network 5 or the load or the alternating current I is terminated _AC AC voltage V _AC Is generated. The fault signal FS is a direct current component, so that, for example, a fault of a current sensor in the inverter 1 is simulated. By determining the alternating current I _AC AC voltage V _AC The switch-off point in time t can be unambiguously determined from when it is substantially zero _A At the switch-off time, the inverter 1 is disconnected from the supply network 5 at the output, for example by opening the disconnection point 4, or at the switch-off time, the ac voltage V is terminated, for example by the control unit 10 _AC AC current I _AC Is generated. In this case, the alternating current I can be checked _AC Or an alternating voltage V _AC Whether it actually continues (to distinguish zero crossings) to zero or within a narrow range, e.g. + -. 0.3A or + -10V around zero. At the switch-off time t _A And fault signal t _F Is the switch-off duration t of the inverter to be checked by means of the switch-off test _Z The switch-off duration can be checked by means of the evaluation unit 12.

By analysing the alternating current I detected by means of the analysis unit 12 _AC AC voltage V _AC A point in time and duration may be determined. For this purpose, the alternating current I can be measured as in FIG. 2 _AC Or an alternating voltage V _AC And analyzed in the analysis unit 12. However, the evaluation unit 12 can also be designed as a conventional oscilloscope, in which no measuring unit is required, but rather the alternating current I can be tapped off directly _AC AC voltage V _AC . The shutdown test can be carried out without having to switch the inverter 1 on or without having to adjust the inverter 1 in terms of hardware. Only the test routine has to be executed in the control unit 10.

Claims

1. Method for carrying out a shutdown test on an inverter (1) which generates an alternating current (I) at an output _AC ) And alternating voltage (V) _AC ) Characterized in that, at a first point in time (t) _T ) Modulating a Trigger Signal (TS) to the alternating current (I) _AC ) Or an alternating voltage (V) _AC ) Wherein the time point at which the Trigger Signal (TS) starts is a first time point (t) _T ) (ii) a Through a first point in time (t) _T ) And a defined duration (t) _D ) Determining a second point in time (t) _F ) (ii) a At a second point in time (t) _F ) I.e. at a first point in time (t) of the Trigger Signal (TS) _T ) After starting, pass throughSaid defined duration (t) _D ) Generating an alternating current (I) with a Fault Signal (FS) by means of an inverter (1) _AC ) Or an alternating voltage (V) _AC ) The fault signal is recognized by the inverter (1) and triggers the inverter (1) to be switched off; and determining the alternating current (I) _AC ) Or an alternating voltage (V) _AC ) Off point in time (t) _A ) Thereby, at the turn-off time point (t) _A ) And a second time point (t) _F ) The difference between them determines the turn-off duration (t) of the inverter (1) _Z )。

2. Method according to claim 1, characterized in that the alternating current (I) generated by the inverter (1) is measured and analyzed _AC ) Or an alternating voltage (V) generated by the inverter (1) _AC ) In order to determine a first point in time (t) _T ) And/or a switch-off time point (t) _A )。

3. Method according to claim 1 or 2, characterized in that the first point in time (t) is compared _T ) Synchronous to alternating current (I) _AC ) Or an alternating voltage (V) _AC ) At zero crossings of the grid.

4. Method according to claim 3, characterized in that the second point in time (t) is compared with _F ) Synchronous to alternating current (I) _AC ) Or an alternating voltage (V) _AC ) At zero crossing of (c).

5. A device for carrying out a shutdown test on an inverter (1) has a control unit (10) which is designed to control a switching device (2) of the inverter (1) for generating an alternating current (I) at an output _AC ) And alternating voltage (V) _AC ) Characterized in that the control unit (10) is configured for at a first point in time (t) _T ) Controlling a switching device (2) of an inverter (1) in order to modulate a Trigger Signal (TS) to an alternating current (I) _AC ) Or an alternating voltage (V) _AC ) Wherein the time point at which the Trigger Signal (TS) starts is a first time point (t) _T ) (ii) a The control unit (10) is constructedIs made to pass through a first point in time (t) _T ) And a defined duration (t) _D ) Determining a second point in time (t) _F ) And at a second point in time (t) _F ) I.e. at a first point in time (t) of the Trigger Signal (TS) _T ) The defined duration (t) after the start _D ) Controlling a switching device (2) of an inverter (1) in order to generate an alternating current (I) with a Fault Signal (FS) _AC ) Or an alternating voltage (V) _AC ) (ii) a Performing a safety function in the inverter (1), said safety function being designed to detect a Fault Signal (FS) and to trigger a shutdown of the inverter (1); and an evaluation unit (12) is provided, which is designed to determine the alternating current (I) _AC ) Or an alternating voltage (V) _AC ) Off point in time (t) _A ) And is controlled by the time point (t) of turn-off _A ) And a second point in time (t) _F ) The difference between them determines the turn-off duration (t) of the inverter (1) _Z )。

6. Device according to claim 5, characterized in that a measuring device is provided, which is configured for measuring the alternating current (I) generated by the inverter (1) _AC ) Or an alternating voltage (V) generated by the inverter (1) _AC ) And the evaluation unit (12) is designed to evaluate the measured alternating current (I) _AC ) Or the measured alternating voltage (V) _AC ) In order to determine a first point in time (t) _T ) And/or a switch-off time point (t) _A )。

7. Device according to claim 5, characterized in that the analysis unit (12) is designed as an oscilloscope which is configured for recording an alternating current (I) _AC ) Or an alternating voltage (V) _AC ) In order to determine a first point in time (t) _T ) And/or a switch-off time point (t) _A )。